1. Field of the Invention
The present invention relates to a lithium ion capacitor.
2. Description of the Related Art
Internal resistance of a lithium ion capacitor is a cause of energy loss when the capacitor is charged or discharged. Particularly with capacitors used for large-current discharge applications, their internal resistance has significant impact on capacitor characteristics. Many of the factors that increase the internal resistance of a capacitor are due to the electrode, electrolyte solution and separator constituting the capacitor. As a way to reduce the internal resistance of the capacitor, therefore, lowering the resistance of each capacitor member has been considered. Methods to lower the resistance of the electrode include adding a substance offering excellent conductive property to the electrode and controlling the electrode structure (refer to Patent Literature 1 and 2, for example). With these methods, however, it is difficult to maintain the original capacity without increasing the electrode thickness or capacitor size. As for lowering of the resistance of the electrolyte solution, on the other hand, an electrolyte solution offering good conductivity and a low-viscosity electrolyte solution have been considered (refer to Patent Literature 3, for example). However, solving the aforementioned problem with these methods is difficult because the withstand voltage characteristics and internal resistance of the capacitor are in a mutually exclusive relationship. Furthermore, film thickness reduction has been considered for the electrode and separator (refer to Patent Literature 4, for example). However, this method reduces operability in the manufacturing process because the member strength becomes weak.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.